PROJECT SUMMARY The eukaryotic second messenger 2',3'-cGAMP is produced by cGAS in response to DNA within the host cell cytoplasm. In response to DNA derived from bacterial and viral infection cGAMP initiates host inflammation to clear infection, while sensing of self-derived DNA has been implicated in autoimmune disorders including Systemic Lupus Erythemytosus and Aicardi-Goutieres Syndrom. Current biological effects of cGAMP are attributed to its interaction with the only known binding protein STING. Interestingly, several recent studies in bacterial, viral, and tumor immunity have revealed a crucial role for cGAS, whereas loss of STING has moderate or no biological consequence on disease outcome. Furthermore, certain cell types do not produce STING but exhibit cGAS expression. Together, these observations have led to the hypothesis that cGAMP produced by cGAS has STING-independent targets that contribute to its role in immune signaling. A chemical proteomics approach has identified previously unrecognized cGAMP binding proteins. This project aims to detail the molecular interaction of these novel receptors and the biological significance using a viral model of infection. Together the studies outlined here will significantly broaden the molecular understanding of cGAS- cGAMP mediated immune modulation with important consequences on infectious, malignant, and autoimmune diseases.